1. Field of the Invention
The present invention relates to a camera having a lens assembly for adjusting a focal length and, more precisely, it relates to a mechanism for moving groups of focus adjusting lenses.
2. Description of Relates Art
In a conventional two-focus lens assembly of a known compact camera, two focuses are given by respective different lens systems. Namely, the two-focus optical system has a master lens group which moves in an optical axis direction and can not move to deviate from the optical axis, and a conversion lens group which can move to deviate from the optical axis. At one of the two focal lengths, the imaging optical system includes the master lens group only, and the imaging optical system includes both the master lens group and the conversion lens group at the other focal length. Accordingly, it is necessary to provide a plurality of conversion lens groups in order to realize three or more focal lengths in the arrangement of the two-focus lens assembly mentioned above. This results in a complicated lens construction and a complicated and large mechanism for moving the conversion lens groups. It is next to impossible to realize more than two multi-focuses by the conventional two-focus lens camera.
A zoom lens which can successively vary the focal length essentially has two pairs of variable power lenses (focal length adjusting lenses) which more close to and away from each other to successively vary the focal length. Usually, a cam ring is used to move the variable power lens assembly.
However, the known zoom lens has many precise optical elements including a cam ring, resulting in increased manufacturing cost.